Iowa Highway 78 (Iowa 78) is a 59-mile-long (95 km) state highway which runs from east to west in southeastern Iowa. The route begins east of Martinsburg at Iowa Highway 149, and ends at U.S. Highway 61 east of Morning Sun. The route has existed since the 1920s, when it was a short spur route between Olds and Winfield. By the 1950s, the route reached its current extents.